The gliding behavior of Myxococcus xanthus cells is controlled by two multigene systems, A and S, which encode information for adventurous and social behaviors, respectively. The S system can be genetically disrupted through mutation, such as a dsp mutation, or phenotypically disrupted by treating cells with the diazo dye Congo red (Arnold and Shimkets, J. Bacteriol. 170:5765-5770, 1988). One of the functions controlled by the S system is cell agglutination. Immediately after the induction of agglutination, wild-type cells begin to form aggregates, and within 30 min the cells are packed side-to-side in clumps containing thousands of cells. Changes in the cohesive properties of S+ cells are correlated with changes in the topology of the cell surface observed by electron microscopy. Two types of cell-associated appendages were observed on wild-type cells: thin filaments (ca. 5 nm in diameter), which have been called fimbriae or pili, at one cell pole, and thick, flaccid ifiaments (ca. 50 nm in diameter), referred to as fibrils, at both the sides and tips of cells. Cohesion was correlated with the secretion of the thick fibrils, which coat the cell surface and form an extracellular matrix in which the cells are interconnected. Several lines of evidence suggest that these thick fibrils are involved in cohesion. First, Dsp cells were unable to agglutinate or secrete this extracellular material. Second, wild-type cells which were treated with Congo red neither agglutinated nor secreted the extracellular fibrils. Finally, removal of the Congo red from wild-type cells restored cohesion and also restored production of the thick fibrils. Attempts to estimate the efficiency with which two cells cohered following collision suggested that under optimal conditions, one in three collisions resulted in stable contact. The collision efficiency decreased linearly as the cell density increased, suggesting a cell density-dependent regulation of cohesion. Some aspects of gliding behavior can be explained in terms of an inducer and an inhibitor of S motility.

Three common finishing treatments of stainless steel that are used for equipment during poultry processing were tested for resistance to bacterial contamination. Methods were developed to measure attached bacteria and to identify factors that make surface finishes susceptible or resistant to bacterial attachment and biofilm formation. Samples of the treated surfaces (sand-blasted, sanded, and electropolished) were exposed to natural bacterial populations from chicken carcass rinses to allow growth of bacteria and development of biofilms on the surfaces. The kinetics of bacterial growth during surface exposure was followed by UV-visible spectrophotometry, and counts of bacteria and early biofilm formation were measured following scanning electron microscopy (SEM). The surface morphology of the samples was analyzed by atomic force microscopy (AFM) with samples from each of the batches of treatments used in the SEM studies. Relative differences in the surface morphology, including fractal dimensions, Z ranges, roughness, and other measurements corresponded by treatment with the differences in reduction of bacterial counts shown by SEM. The surface types varied in affinity for bacteria, and both physical and electrochemical treatments improved resistance of stainless steel to bacterial attachment. Electropolished stainless steel was the least rough surface and showed significantly fewer bacterial cells and beginning biofilm formations than the other treated surfaces. Food safety could be improved if bacterial populations could be reduced during processing by increasing the use of materials that are resistant to bacterial contamination. These findings will aid equipment manufacturers and processors in selecting materials and finishes that are most resistant to bacteria and biofilm formation.

Growth and carcass measurements were made on 2,411 Hereford steers slaughtered at a constant weight from a designed reference sire program involving 137 sires. A second data set consisted of ultrasound measures of backfat (USFAT) and longissimus muscle area (USREA) from 3,482 yearling Hereford cattle representing 441 sires. Restricted maximum likelihood procedures were used to estimate genetic parameters among carcass traits and live animal weight traits from these two separate data sets. Heritability estimates for the slaughter weight constant steer carcass backfat (FAT) and longissimus muscle area (REA) were .49 and .46, respectively. In addition, FAT had a negative genetic correlation with REA (-.37), weaning weight (-.28), and yearling weight (-.13) but positive with marbling (.19) and carcass weight (.36). Marbling was moderately heritable (.35) and highly correlated with total postweaning average daily gain (.54) and feedlot relative growth rate (.62). Heritability estimates for weight constant USFAT and USREA were .26 and .25, respectively. The genetic correlation between weight constant USFAT and USREA was positive (.39), indicating that in these young animals USFAT does not seem to be an indication of maturity. Mean USFAT measures and variability were small (.48 +/- .17 cm, n = 3,482). Results indicate that carcass fat on slaughter steers and ultrasound measures of backfat on young breeding animals may have different relationships with growth and muscling. These relationships need to be explored before wide scale selection based on ultrasound is implemented.

The function of molecules associated with the cell surface may be determined by examining the phenotype of cells treated with inhibitors specific to these cell surface molecules. This strategy was used to examine the function of the major Congo red receptor of the myxobacterium Myxococcus xanthus, which has a developmental cycle that involves social interactions among cells. A class of social motility mutations (A+ S-), known as dsp, may inhibit the same subcellular component as Congo red because the phenotype of wild-type cells which had been treated with Congo red resembled in several ways the phenotype of the Dsp mutants. First, Congo red inhibited agglutination of wild-type cells, whereas Dsp cells were incapable of agglutinating, even in the absence of Congo red. Second, Congo red inhibited fruiting body formation by wild-type cells and reduced the yield of myxospores. Untreated Dsp cells were unable to form fruiting bodies and produced few myxospores. Third, Congo red reduced the rate of wild-type gliding motility to a level comparable to that of untreated Dsp cells, but did not inhibit the A motility of Dsp cells. Finally, binding studies showed that Dsp cells lacked the major Congo red receptor. Wild-type cells bound Congo red with an apparent association constant of 2.4 X 10(5) M-1, while Dsp cells bound it with an apparent association constant of 8.5 X 10(3) M-1. Binding of Congo red to wild-type cells was saturated in less than 10 min and was reversible when excess Congo red was removed. These results suggest that the Congo red receptors are controlled by the S motility system and that these receptors are involved in cell cohesion, social motility, and fruiting body formation.

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Electronic nose technology has previously been applied to the assessment of the quality of red meats, pork and ®sh, but not poultry products. In the present study the ability of the electronic nose to assess the microbiological quality of raw poultry meat as a function of storage time and temperature was investigated. Four types of chicken pieces (boneless breast with and without skin, wings and thighs) were stored for up to 2 days at 13°C (the maximum allowable temperature in poultry processing environments) or for up to 5 days at 4°C (refrigeration temperature for raw poultry products prior to shipping or further processing). Saline rinses of meat samples were serially diluted in tryptic soy broth to 10 À10 . The rinses and their associated serial dilutions were analysed on an electronic nose with 12 metal oxide sensors in order to determine the speci®city and sensitivity respectively of the assay. Principal component analysis (PCA) maps of the data con®rmed that the electronic nose could differentiate volatile compounds associated with individual types of meat samples properly stored at 4°C from those maintained at processing temperature, 13°C, for a comparable time, even as early as day 1 of storage. Differences in headspace gases from any type of meat sample stored at one temperature could also be determined with increased storage time. However, data from samples stored at 4°C clustered more tightly in PCA maps than those associated with samples maintained at 13°C, indicating a greater diversity in volatile compounds at the higher temperature. We have shown herein that the electronic nose can detect changes in the volatile compounds associated with chicken meat based on product storage time and temperature; the technology can assess length of sample storage as well as deviation from refrigeration temperature. Published in

Campylobacter jejuni is the most frequently reported cause of foodborne illness in the United States, but its survival outside the host is poor. The objective of this research was to examine the formation and composition of biofilms by C. jejuni alone and within mixed bacterial populations from the poultry-processing environment. C. jejuni growth was assessed with four media, two temperatures, and two atmospheric conditions to develop culture methods for liquid media that would allow growth within the biofilms. Growth kinetics was followed at four cell densities to determine temporal compatibility within biofilm mixtures. Analysis of the biofilms by confocal laser scanning microscopy showed that C. jejuni formed a biofilm when incubated without other bacteria. The average surface area of stainless steel covered by C. jejuni increased by 50% from 24 to 48 h, remained level to 96 h, and then decreased by 88% by 168 h. C. jejuni and mixed bacterial populations formed biofilms during incubation periods of up to 7 days. The area of the mixture was significantly greater than for C. jejuni alone at 24 h, was approximately the same at 48 h, and was significantly less by 168 h. When incubated with either of two initial inoculum densities of other bacteria, the number of C. jejuni was enhanced after 24 h. The intensity of fluorescence and cell viability were monitored by epifluorescence microscopy. This study provides the basis for studying interactions of Campylobacter spp. with other bacteria in the environment, which will aid in the design of effective intervention strategies.

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